All through the 00s, I worked in a Comparative Immunology lab trying to figure out why some cohorts of creatures got sick and others did not. We got through so much money trying to work out why Campylobacter was tolerated by the chicken's immune system but caused such a dramatic <bloooargh> reaction when we eat a dodgy chicken nugget. After years of talking about the idea, the lab started to work with Irish women who were exposed to HCV during the anti-D scandal but never got hepatitis. They must have had something special in their innate immune toolkit that blatted the virus before it could start reproducing. They [I'd left by then] tried to locate that p'arful magic because it would be really handy for developing new therapies against the condition . . . which resides in nearly 200 million people worldwide.
When Vice tells me that there are no cases of people born blind who are schizophrenic, my first response was to question the veracity of the statement. Because No cases seemed so unlikely . . . unless . . . it was a Venn Diagram intersection issue for two rare conditions: (rare x rare) might approach zero? That tasked me to learn what are those rates.
Schizophrenia is not uniformly rare: rates per country vary from 0.3% to 0.7%. That is a lot of people who need some form of care, attention or medication: 235,000 in Ireland. Compare that to rare like Batten's Disease [N = 4 in Ireland] or Cystic Fibrosis [N = 1,300]. Another way of looking at the impact per country is the DALY - disability adjusted life year; a metric clearly related to the QALY. This shows that schizophrenia is not so much fatal but that it does impact on the quality of your life. And the lives your carers and loved ones, although I'm not sure if / how that is incorporated in the following global view. Some untoward is happening in Indonesia and the Pacific islands while Europeans are less beset by schizophrenia.
Congenital blindness is much less common than schizophrenia. Something like 200 cases of born-blind children in Ireland from all causes. A small enough number that Goggin and O'Keefe (1991) could observe and interview almost all of them. It is really not unexpected therefore that we have no cases of blind schizophrenia in Ireland. There are insufficient numbers for the [dis]association to be statistically significant. Then again Ireland is a small country (1% of the EU population or 1/1000 for the whole world). If there are 20,000 congenitally blind EU kids, we expect 200 of them to be schizophrenic and there are none so there is a case to answer.
They say that we get 70% of our incoming information through the eyes and we process that weleter of photonic information down to manageable proportions. Visual illusions as well as being a staple for cchildren's quiz books, allow us to see / not-see the compromises the brain makes to make sense of the world out there. Psychologist RD Laing famously asserted that "Insanity - a perfectly rational adjustment to an insane world" and "Schizophrenia cannot be understood without understanding despair.". Maybe therefore, if you really damp down the incoming roil of conflicting information then you're less likely to be forced to compromise your sanity to make sense of it. Just think of irony - of which I am really over fond - where the meaning of the words is belied by the intonation or facial expression. Or picking up a lie or a false laugh by the subconscious processing of the other person's face.
Anyway it might make you reflect with wonder about the human condition - how things which we put quite confidently into different bins are actually unexpectedly entwined.